rtk-ai/rtk · error

hg diff must parse

Error message

hg diff must parse

What it means

Test panic from `condense_unified_diff_strict(fixture).expect("hg diff must parse")` in src/cmds/git/diff_cmd.rs:6054. condense_unified_diff_strict returns Result and the test asserts the real-world `hg diff` fixture (tests/fixtures/diff/hg_diff_raw.txt) parses into condensed [file] entries. A panic means the Mercurial diff condenser failed to latch on the fixture and returned an error (or a raw passthrough signal) instead of structured output — a regression in the diff parsing state machine.

Solutions

1. Run `cargo test hg_diff_echo_carries_one_revision -- --nocapture` to see the parser error/raw output
2. Compare the fixture against the header-detection regexes/state transitions that changed in the recent commit
3. Restore latch behavior for `diff -r <rev> <path>` echoes and re-run the full diff test module

Example fix

// before (header matcher only accepts git-style two-path headers)
if line.starts_with("diff --git ") { ... }
// after (also accept hg echo with optional single -r)
if line.starts_with("diff --git ") || line.starts_with("diff -r ") || line.starts_with("diff ") { ... }

// pre-check in tests/CI before asserting
let fixture = include_str!("../../../tests/fixtures/diff/hg_diff_raw.txt");
assert!(fixture.contains("diff -r "), "fixture must contain hg echo header");

fn parsed_or_none(r: Result<String, ParseError>) -> Option<String> { r.ok() }

let out = match condense_unified_diff_strict(fixture) {
    Ok(o) => o,
    Err(e) => panic!("hg diff must parse: {e}\nfixture head: {:?}", &fixture[..200]),
};

When it happens

Trigger: Running `cargo test` after changes to condense_unified_diff_strict or its hg handling; the fixture's `diff -r <rev>` echo, a/ b/ prefixes, quoted/tabbed filenames, or binary fact are no longer recognized.

Common situations: Refactoring the unified-diff parser, renaming file-header detection, or tightening the revision-echo latch so hg's single `-r` echo no longer closes/validates the diff region.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• hg log -p must parse
• must parse
• hg export must parse
• intact series must parse
• invalid ctest result prefix regex

AI-assisted analysis of rtk-ai/rtk@0924356b4c (2026-09-19). Data as JSON: /api/errors/246fdfa52436ae8a. Report an issue: GitHub.

Appendix: source

Thrown at src/cmds/git/diff_cmd.rs:6054

        assert!(out.contains("[file] say \"hi\".txt (+5 -0)"), "got:\n{out}");
        assert!(out.contains("[file] tab\there.txt (+5 -0)"), "got:\n{out}");
        // A name holding a newline keeps git's own quoted spelling, with
        // the prefix stripped inside the quotes: one `[file]` line per
        // file, lossless, and spelled as `diff --cc` spelled it.
        assert!(
            out.contains("[file] \"new\\nline.txt\" (+5 -0)"),
            "got:\n{out}"
        );
        assert_eq!(out.matches("[file] ").count(), 11, "got:\n{out}");
    }

    #[test]
    fn hg_diff_echo_carries_one_revision() {
        // Real `hg diff` (not export): `diff -r <rev> <path>` with a single
        // `-r`, names with `a/`/`b/` prefixes, a tab and a `"` in names,
        // and hg's binary fact.
        let fixture = include_str!("../../../tests/fixtures/diff/hg_diff_raw.txt");
        let out = condense_unified_diff_strict(fixture).expect("hg diff must parse");
        for label in [
            "[file] a and b.txt (+1 -1)",
            "[file] b/blob.bin (binary)",
            "[file] b/inb.txt (+1 -1)",
            "[file] back\\slash.txt (+1 -1)",
            "[file] café.txt (+1 -1)",
            "[file] colon: x.txt (+1 -1)",
            "[file] it's.txt (+1 -1)",
            "[file] say \"hi\".txt (+1 -1)",
            "[file] say \"hi\".txt.bin (binary)",
            "[file] tab\there.txt (+1 -1)",
            "[file] tab\there.txt.bin (binary)",
            "[file] trail .txt (+1 -1)",
        ] {
            assert!(out.contains(label), "missing {label:?}:\n{out}");
        }
        // `hg log -p`: a `changeset:` prologue at column 0 before every
        // changeset, then the two-`-r` echo; used to go raw on the latch.

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